Just going by the averages in the table I posted, and if my math is right...
ISU's average kickoff was 57.9 yards with an average net of 39.6 yards, so the average return would be 57.9 - 39.6 = 18.3 yards. However, that doesn't match up with (1056)/(74-12)=17.0 yd/return. Maybe I don't understand the table correctly.
Assuming kickoff from the 35 yd line with a 57.9 kickoff, the receiving team would get the ball at the 7.1 yd line.
Adding the 18.3 average return would put the average starting position at the 25.4 yd line.
Adding the 17 yd average return would put the average starting position at the 24.1 yd line.
Yeah, I was having a bit of trouble understanding what each item in that table meant. But I think the table is missing a key statistic - the fair caught kickoffs that go back to the 25 yard line, unless they are counted as touchbacks. They should be, but I feel like we would have way more than 12 if they were counted. We also don't know for sure how those numbers are being counted in the statistics - is a fair catch on the 10 yard line counted as a 0 yard return, a 15 yard return, or a touchback?
But let's say you're right and the average is correct at an average start of 25. That's still a little misleading. The average start may be the 25 yard line, but that doesn't mean it's the most common start. Let's look at the K-State game for example. They had 3 kick returns for a total of 104 yards per ESPN's stats. That's an average return of 34.6 yards per return. However, that includes one 93 yard return greatly increasing the average. The returns were 4 yards, 7 yards, and 93 yards. If you assume the average kickoff of 58 yards starting from the 35, then the ball typically landed at the 7 yard line. So 2/3 of the time when a return was attempted the other team started from inside the 15 yard line. 1/3 times we let them break loose.
The K-State game is an extreme example, but if you look at it over the season and had a list of each starting position after the kickoff for the opposing team I believe you'll see that the majority of the time they started their drives from inside the 25 and the vast majority inside the 30. It seems to me that ever since the 25 yard line touchback rule was implemented, our kickers started aiming to hit between the 5-10 yard line to bait a return. In the past, you could see that in situations where we couldn't afford a possible good return, we kicked deeper. I'm not sure if this year we had a guy with the big leg to consistently hit it that deep though.